U.S. patent application number 11/799159 was filed with the patent office on 2007-11-08 for zeolites with uniform intracrystal textural pores.
This patent application is currently assigned to Board of Trustees of Michigan State University. Invention is credited to Thomas J. Pinnavaia, Hui Wang.
Application Number | 20070258884 11/799159 |
Document ID | / |
Family ID | 38668251 |
Filed Date | 2007-11-08 |
United States Patent
Application |
20070258884 |
Kind Code |
A1 |
Pinnavaia; Thomas J. ; et
al. |
November 8, 2007 |
Zeolites with uniform intracrystal textural pores
Abstract
Zeolites with uniform intracrystal textural pores between 1 and
10 nm are described. Intracrystal pores, an alumina source and a
silica source are reacted in the presence of a silane modified
polymer as a porogen and the reaction product is calcined to form
the zeolite. The zeolites are useful in catalytic reactions and
adsorption processes.
Inventors: |
Pinnavaia; Thomas J.; (East
Lansing, MI) ; Wang; Hui; (East Lansing, MI) |
Correspondence
Address: |
Ian C. McLeod;IAN C. MCLEOD, P.C.
2190 Commons Parkway
Okemos
MI
48864
US
|
Assignee: |
Board of Trustees of Michigan State
University
East Lansing
MI
|
Family ID: |
38668251 |
Appl. No.: |
11/799159 |
Filed: |
May 1, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60797216 |
May 3, 2006 |
|
|
|
Current U.S.
Class: |
423/700 ;
502/70 |
Current CPC
Class: |
B01J 29/084 20130101;
C01B 39/24 20130101; B01J 29/40 20130101; B01J 35/10 20130101; C01B
39/04 20130101; C10G 11/05 20130101; B01J 37/0018 20130101; C01B
39/40 20130101; B01J 35/1061 20130101 |
Class at
Publication: |
423/700 ;
502/70 |
International
Class: |
B01J 29/06 20060101
B01J029/06; C01B 39/00 20060101 C01B039/00 |
Claims
1. A process for forming a calcined zeolite with uniform
intracrystal textural pores, which comprises: (a) reacting a
porogen comprising a silane modified polymer, wherein the polymer
is covalently linked to the silane modifier and the mass of polymer
per mole of silane modifier is at least 100 grams per mole, in a
mixture of an alumina source and a silica source to form a
porogen-linked aluminosilicate reaction mixture; (b) digesting the
reaction mixture to form zeolite crystals with the silane modified
porogen occluded within the crystals; and (c) removing the occluded
intracrystal porogen from the zeolite crystals by calcination to
form the calcined zeolite with the uniform intracrystal pores.
2. The process of claim 1 wherein the zeolite containing the
occluded intracrystal porogen is calcined at a temperature between
about 500.degree. and 850.degree. C.
3. The process of claim 1 wherein the porogen is a reaction product
of an amine substituted polymer with at least one NH group with an
aliphatic epoxy silane.
4. The process of any one of claims 1, 2 or 3 wherein the silane is
3-glycidoxypropyl-trimethoxysilane.
5. The process of any one of claims 1, 2, or 3 wherein the polymer
is selected from the group consisting of a polyethyenimine and an
alpha, omega-polypropylene oxide diamine.
6. A calcined zeolite with uniform intracrystal textural pores
which are about 1 to 10 nm in at least one dimension.
7. The zeolite composition of claim 6 with an average pore size
value for the intracrystal textural pores centered between 1 and 10
nm and with the pore size distribution centered around the average
pore size value being between 1 and 10 nm.
8. The zeolite compositions of claims 6 and 7 for which the
intracrystal textural pores provide a pore volume of at least 0.05
cc per gram.
9. A process for forming a polymer modified trialkoxysilane which
comprises: (a) reacting an amine-substituted polymer containing at
least one NH group with an aliphatic epoxy silane in the presence
of an organic solvent; and (b) separating the solvent from the
solvent to form the polymer modified silane.
10. A polymer modified aliphatic silane with a polymer mass per
mole of silane of at least 100 grams per mole of silane.
11. A process comprising cracking a hydrocarbon feedstock in the
presence of a catalyst composition comprising a catalytically
active material selected from the group consisting of the zeolite
compositions of claims 6 and 7, amorphous aluminosilicates and
zeolitic, crystalline aluminosilicates, and a matrix material.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims benefit to U.S. Provisional
Application Ser. No. 60/797,216, filed May 3, 2006, which is
incorporated herein by reference in its entirety.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] Not Applicable.
BACKGROUND OF THE INVENTION
[0003] (1) Field of the Invention
[0004] The present invention relates to calcined zeolites, which
are aluminosilicates, with uniform intracrystal mesopores. In
particular, the present invention relates to a process for forming
the zeolites by reacting porogens comprising a modified silane,
wherein a polymer is covalently linked to silicon in the silane,
with a silica source and an alumina source. The present invention
also relates to novel porogens. In particular, the present
invention relates to calcined zeolite crystals with uniform
intracrystal pores of between about 1 and 10 nm in one
dimension.
[0005] Further, the present invention relates to a process for
forming the zeolites by the use of a Si covalently linked organic
polymer silane as a porogen in the formation of the zeolite.
[0006] (2) Description of the Related Art
[0007] Zeolites are crystalline aluminosilicates that are widely
used in industry as catalysts and molecular sieves (Corma, A.
Chemical Review 97, 2373-2419 (1997)). These materials have
crystalline open framework structures with well defined micropore
windows that range in size from 0.3 to 1.2 nm, depending on the
type of framework structure. Molecules smaller than the pore
openings are capable of entering the framework pores. The small
framework micropores limit the usefulness of zeolites for catalytic
reactions and adsorption processes when the size of the guest
molecule is larger than the pore size of the zeolite. Even when the
guest molecule is smaller than the framework pore size of the
zeolite, the diffusion rate of reactants and products into and out
of the channels can be slow, thereby limiting catalytic activity
and selectivity.
[0008] Open framework structures with pore sizes of a few
nanometers, ie., <10 nm, in dimensions are expected to function
as size or shape selective catalysts for the conversions of large
molecules. For instance, using non-zeolitic mesostructured
aluminosilicates for the catalytic cracking of polymeric
macromolecules, (Aguado et al., Energy and Fuels 1997, 11,
1225-1231) have shown that uniform mesopores a few nanometers in
diameter provide higher yields of liquid fuels than are obtained
using the same aluminosilicate composition with much larger and
less uniform mesopore distributions. Thus, zeolites with uniform
small mesopores or uniform large micropores can be expected to
function as selective catalysts for the cracking of large petroleum
molecules and other catalytic conversions of large molecules.
However, zeolites with these desired pore size properties are
unknown. Moreover, the kinds of shape-selective mesostructured
aluminosilicates studied by Aguado et al. lack atomic order (i.e.
the materials are amorphous) and therefore, lack the desire acidity
and hydrothermal stability needed for the efficient cracking of
large molecules.
[0009] There have been many attempts to provide for zeolites with
uniform large micropores (1.2-2.0 nm) or small mesopores (2-10 nm).
Efforts to crystallize stable zeolites with framework pores larger
than about 1.2 nm have been unsuccessful. Consequently, attention
has been directed at introducing textural mesoporosity into known
zeolite structures with conventional small framework micropores.
Textural porosity is distinct from framework porosity, because it
is independent of the crystal structure of the zeolite. The
introduction of textural porosity in zeolite compositions has been
achieved in many ways. As will become evident from the discussion
below; however, the methods disclosed thus far for the introduction
of textural porosity in zeolites inevitably results in very broad
textural pore size distributions and with average textural pore
sizes (>10 nm) that are far larger than is desired for selective
large molecule adsorption and catalysis.
[0010] One (1) approach to achieving textural pores in zeolites is
to make the fundamental crystal size of the zeolite very small,
preferably less than 100 nm. Nanosized zeolites can be synthesized
in low yields in the form of clear solutions by kinetic control of
the crystallization process (Bein, T., et al., Angewandte
Chemie-International Edition 41(14), 2558-2561 (2002); Martens, J.
A., et al., Angewandte Chemie-International Edition 40 (14),
2637-2640 (2001)), (Martens, J. A., et al., Journal of Physical
Chemistry 103(24), 4972-4978 (1999)). If the nanoparticles are
subjected to nano-filtration or ultracentrifugation, and isolated
in powdered form, the voids formed between the nanoparticles
represent textural mesopores. However, the interparticle mesopores
have a very broad pore size distribution and the average textural
pore size is much larger than 10 nm. The broad mesopore
distribution limits and even precludes product or reactant
selectivity based on molecular sizes or shape. The value of
interparticle mesopores between nanoparticles lies primarily in
speeding-up reaction rates through improved molecular diffusion
through the framework pores of the crystals. For example, nanosized
zeolites have been observed to show higher catalytic performance
than conventional monolithic zeolites due to the larger external
surface areas and the more rapid diffusion of reactants and
products through crystals that are typically smaller than a few
hundred nanometers in size. (Yamamura, M., et al., Zeolites 14,
643-649 (1994); Vogel, B., et al., Catalysis Letters, 79, 107-112
(2002); Landau, M. V., et al., Industrial & Engineering
Chemistry Research 42, 2773-2782 (2003); and Zhang, P. Q., et al.,
Catalysis Letters 92, 63-68 (2004)).
[0011] Aggregated or intergrown zeolites nanoparticles with
interparticle mesopores can be produced by growing the crystals in
the nanopores of a carbon template, a process also as zeolite
nanocasting. For instance, nanocrystalline ZSM-5 with different
crystal sizes were synthesized in the confined spaces provided by a
carbon black matrix (Schmidt, I., et al., Inorganic Chemistry
39(11), 2279-2283 (2000); Jacobsen, C. J. H., et al., Chemical
Communication 8, 673-674 (1999)). Also, colloid-imprinted carbons
have been used as a template for the nanocasting of aggregated and
intergrown nano-sized ZSM-5 with fundamental crystal sizes from 12
to 90 nm (Kim et al., Chemical Communication 15, 1664-1668 (2003)).
The resulting nanosized zeolite exhibited mesopores that arise from
voids between aggregated and intergrown nanocrystals. Although the
fundamental crystal size of the resulting nanocasted zeolite is
very small, the packing or aggregation of the crystallizes is
non-uniform, resulting in interparticle mesopores that also are
non-uniform and larger on average than the size of the fundamental
particles themselves. In a related approach using carbon aerogel as
a template, Tao and co-workers (PCT International Application WO
2003104148; Tao, Y., et al., Journal of the American Chemical
Society 125(20), 6044-6045 (2003)) synthesized ZSM-5 with an
average textural mesopore size centered at 11 nm and a width at
half height of 3 nm. This is the smallest and narrowest
interparticle textural mesoporosity yet reported for a crystalline
zeolite.
[0012] There are several disadvantages to the nanocasting approach
to the formation of interparticle mesoporous zeolites. Firstly,
little or no mesoporosity is generated below 5 nm, the size regime
most desired for size and shape of selective chemical catalysis.
Another disadvantage of carbon templating methods to obtaining
nanosized mesoporous zeolites is the need to provide for nanosized
carbon templates for forming the nanoparticles and then destroying
the carbon template through calcination.
[0013] Another strategy to obtaining mesoporous zeolites involves
the formation of mesopores within, as opposed to between, zeolite
crystals. The intracrystal textural mesoporous zeolites can be
achieved by steaming and chemical leaching of monolithic zeolites
crystals to remove zeolite mass, leaving behind mesopores. (Groen,
J. C., et al., Chemistry-A European Journal 11(17), 4983-4994
(2005); Groen, J. C., et al., Microporous and Mesoporous Materials
87 (2), 153-161 (2005)). These techniques usually produce
intracrystal pores much larger than 10 nm. Also, the resultant
pores are not especially uniform in diameter.
[0014] In yet another approach to the formation of intracrystal
mesopores, attention had been focused on the incorporation of
carbon nanoparticles into zeolite crystals as they crystallize. The
subsequent removal of the occluded carbon particles by calcination
results in intracrystal mesopores that replicate the size and shape
of the templating carbon. In particular, carbon black particles
have been used as a templating agent to form intracrystal mesopores
in zeolites (Jacobsen, C. J. H., et al., Journal of the American
Chemical Society 122(29), 7116-7117 (2000); Janssen, A, H., et al.,
Microporous and Mesoporous Materials 65(1), 59-75 (2003)). Carbon
nanotubes also have been used as nanoparticle templates for the
formation of intracrystal mesopores (Schmidt, I., et al., Chemistry
of Materials 13(12), 4416-4418 (2001)). But due to the weak
interaction between carbon and a silica matrix, the nanoparticle
carbon templates were often extruded out of the zeolite crystal
during crystallization, resulting in nanosized zeolite products
with interparticle mesoporosity rather than intraparticle
mesoporosity. Even when carbon nanoparticles were successfully
occluded into the zeolite crystals using special gel processing
techniques, the mesopore size distribution could be no better than
the particle size fidelity of the occluded carbon nanotubes, which
are notorious for forming aggregates with a broad size
distribution.
[0015] There are two (2) major disadvantages associated with the
above approaches to the formation of zeolites with textural
mesoporous. The first one is that, with the exception of the
zeolite formed by nanocasting in a carbon aerogel (c.f., Tao et
al.), the resulting mesopores, whether inter- or intra-particle
mesopores, typically are widely distributed in size. The uniformity
of mesopore is dependent on the nanocrystal size or the carbon
porogens, both of which tend to be irregular in both size and
shape. Therefore, the resultant zeolites reflect the same broad
distribution of mesopores, which is not suitable for shape or size
selective catalytic conversions. Furthermore, even when the
mesopore size distributions is comparatively narrow as in the case
of zeolites formed through the use of carbon aerogels as templates
(c.f., Tao et al), there is little or no pore volume or large
micropore range is provided in the 1-2 nm large micropore range or
in the 2-10 nm small mesopore domain, which is highly desired for
shape or size selective conversions or separations of large
molecules. Moreover, little or no textural mesoporosity has yet to
be disclosed in the size range below 6 nm, where such mesoporosity
is expected to show shape-selectivity in catalytic reactions such
as petroleum cracking and refining.
[0016] Mesostructured aluminosilicates with ordered networks of
uniform pores in the mesopore ranging from 2.about.50 nm have been
considered as potential substitutes for large pore zeolites.
However, due to the absence of atomic order in the mesostructured
framework walls, these compositions lack the desired hydrothermal
stability and acidity for such applications. In an effort to
combine the features of zeolites and mesostructured
aluminosilicates, van Bekkum and co-workers reported a
double-template approach for the synthesis of
zeolite--mesostructured aluminosilicate composites. (van Bekkum,
H., et al., Chemical Communication 2281-2282 (1997); van Bekkum,
H., et al., Chemistry of Materials 13, 683-687 (2001)). Also,
Kaliaguine and co-workers used coating and post-synthesis
crystallization techniques to form composite mixtures of zeolite
nanocrystals dispersed in a mesoporous aluminosilicate support with
amorphous framework walls (Kaliaguine, S., et al., Angewandte
Chemie-International Edition 40(17), 3248-3251 (2001); Kaliaguine,
S., et al., Angewandte Chemie-International Edition 41(6),
1036-1040 (2002)). These composite compositions provide uniform
mesoporosity in combination with a zeolite phase, but the phase
contributing the mesoporosity is not a zeolite. Thus, dispersing
zeolite nanoparticles on mesostructured aluminosilicate supports
also does not provide the zeolitic porosity in the desired large
micropore to small mesopore range for the selective chemical
catalysis of large molecules.
[0017] Organosilanes containing small organo groups have been
previously incorporated into zeolite structures for the purpose of
modifying the chemical or physical surface properties of the
zeolite (Yan, Y. et al., Microporous Mesoporous Materials, 17(15),
347-356 (2005); Tatsumi, T. et al. Chemistry of Materials, 17(15),
3913-3920 2005)). Also, organosilanes have been used to prepare
nanosized zeolite having increased outer surface area (Aguado, J.
et al. WO 2005026050). However, due to the small size of the silane
organo group or the inappropriate ratio of polymer weight to silane
modifier used in these studies, intra-crystalline textural porosity
was neither observed nor anticipated.
OBJECTS
[0018] It is an object of the present invention to provide novel
zeolites with uniform intracrystal mesopores. Further, it is an
object of the present invention to provide novel porogens. Further,
it is an object to provide processes for the preparation of the
porogens and the zeolites which are economical. These and other
objects will become increasingly apparent by reference to the
following description and the drawings.
SUMMARY OF THE INVENTION
[0019] The present invention relates to a process for forming a
calcined zeolite with uniform intracrystal textural pores which
comprises: (a) reacting a porogen comprising a silane modified
polymer, wherein the polymer is covalently linked to the silane
modifier and the mass of polymer per mole of silane modifier is at
least 100 grams per mole, in a mixture of an alumina source and a
silica source to form a porogen-linked aluminosilicate reaction
mixture; (b) digesting the reaction mixture to form zeolite
crystals with the silane modified porogen occluded within the
crystals; (c) removing the occluded intracrystal porogen from the
zeolite crystals by calcination to form the calcined zeolite with
the uniform intracrystal pores. Preferably, wherein the zeolite
containing the occluded intracrystal porogen is calcined at a
temperature between about 500.degree. and 850.degree. C. Most
preferably, the porogen is a reaction product of an amine
substituted polymer with at least one NH group and an aliphatic
epoxy silane. Preferably, the silane is
3-glycidoxypropyl-trimethoxysilane. Further, the polymer is
preferably selected from the group consisting of a polyethyenimine
and an alpha, omega-polypropylene oxide diamine. Further, the
present invention relates to a calcined zeolite with uniform
intracrystal textural pores which are about 1 to 10 nm in at least
one dimension. Still further, preferably an average pore size value
for the intracrystal textural pores is centered between 1 and 10 nm
and with the pore size distribution centered around the average
pore size value being between 1 and 10 nm. Further, wherein the
intracrystal textural pores provide a pore volume of at least 0.05
cc per gram.
[0020] Still further, the present invention relates to a process
for forming a polymer modified trialkoxysilane which comprises: (a)
reacting an amine-substituted polymer containing at least one NH
group with an aliphatic epoxy silane in the presence of an organic
solvent; and (b) separating the product from the solvent to form
the polymer modified silane. Preferably, wherein the invention
relates to a polymer modified aliphatic silane with a polymer mass
per mole of silane of at least 100 grams per mole of silane.
Preferably, the solvents are alcohols containing 1 to 4 carbon
atoms. The reaction temperature is between about 80 and 120.degree.
C.
[0021] Finally, the present invention relates to a process
comprising cracking a hydrocarbon feedstock in the presence of a
catalyst composition comprising a catalytically active material
selected from the group consisting of the zeolite compositions,
amorphous aluminosilicates and zeolitic, crystalline
aluminosilicates, and a matrix material.
[0022] The present provides a process for forming zeolite
compositions with uniform intra-crystalline textural pores,
particularly in the large micropore range between 1.2-2.0 nm and
the small mesopore range between 2 and 10 nm. Moreover, the average
textural pore size typically is less than 6 nm, and the average
pore volume over the stated large micropore and small mesopore
ranges is at least 0.05 cc/g, more typically greater than 0.1 cc/g
and even greater than 0.5 cc/g.
[0023] Still further, the zeolite compositions of the present
invention are ideally suited as a catalyst component for cracking a
hydrocarbon feedstock and for use in a process comprising cracking
a hydrocarbon feedstock in the presence of the catalyst composition
comprising a catalytically active material selected from the group
consisting of the zeolite compositions of the present invention,
amorphous aluminosilicates and zeolitic crystalline
aluminosilicates, and a matrix material.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] FIG. 1 provides the nitrogen adsorption/desorption isotherms
for conventional ZSM-5 zeolite and for MSU-MFI zeolite synthesized
according to Example 2 in the presence of the silane-modified
polyethyleneimine textural porogen MP-25000(5).
[0025] FIGS. 2A to 2D are graphs showing the BJH textural pore size
distributions for MSU-MFI zeolites synthesized with silane-modified
polyethyleneimine porogens of differing molecular weight: (A)
MP-600(5); (B) MP-1800(5); (C) MP-10000(5); (D) MP-25000(5)
according to Example 2. For each zeolite synthesis, the molar ratio
of silicon in the form of TEOS to silicon in the form of
silane-modified porogen was 1.0:0.10.
[0026] FIG. 3 is a TEM image of a thin-sectioned sample of MSU-MFI
zeolite prepared in the presence of the silane-modified
polyethyelenimine porogen MP-25000(5). The low contrast regions of
the imaged particles identify the intracrystal textural pores.
[0027] FIG. 4 is the nitrogen adsorption/desorption isotherms for
conventional zeolite Y and a MSU-Y zeolite synthesized according to
Example 3 in the presence of the textural porogen MP-25000(5).
[0028] FIG. 5 is the nitrogen adsorption/desorption isotherms and
pore size distributions for MSU-MFI zeolites synthesized in the
presence of MP-D2000 and MP-D4000 porogens according to the method
of Example 4.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0029] The aluminosilicate compositions described herein are
ultra-stable and highly acidic mesoporous materials well suited for
the cracking of petroleum molecules and other acid-catalyzed
reactions. The approach to generating uniform intracrystal textural
pores in zeolite crystals makes use of silane-modified polymers as
textural porogens during the synthesis of a desired zeolite
framework. The said porogens covalently link to the growing crystal
through Si--O--Si linkages and become occluded in the crystal as
the crystal continues to grow. The removal of the porogen from the
crystallized zeolite by calcination generates the desired
intracrystal textural pores.
[0030] The ratio of polymer to silane modifier is selected to be
effective as a porogen for the formation of textural and
intra-crystalline pores in the large micropore range 1.2-2.0 nm and
the small mesopore range 2.0-10 nm. The weight of polymer or
polymer segment per mole of silane modifying agent is preferably at
least about 100 grams of polymer per mole of silane modifier. The
silane modifier, the polymer and the linkage between the silane
modifier and the polymer are selected to be stable under the basic
pH conditions needed to crystallize a zeolite framework.
Nitrogen-carbon bonds between the silane modifier and the polymer
are preferred linkages, but the present invention is not limited to
such linkages.
[0031] The silane reagents suitable for modification of polymer
porogens are of the type X.sub.3SiL, where one or more X groups,
preferably all three X groups, are hydrolyzable and effective in
forming bridging Si--O--Si linkages to the external surfaces of a
growing zeolite crystal during zeolite synthesis. Preferred
hydrolyzable X groups are selected from the groups comprising
alkoxides or halides. The moiety L of the silane modifier is a
non-hydrolyzable organo group linked to silicon through a Si--C
covalent bond and is effective in reacting through covalent bond
formation with one or more reactive groups on a polymer porogen.
The silane group binds to the surface of the growing zeolite
crystal during synthesis through Si--O--Si linkage formation and
the growing crystal encapsulates the porogen as it continues to
grow in size. One (1) or more silane units may be linked to the
polymer. The organofunctional group L used to link the polymer
porogen to the silane modifier, as well as the polymer porogen
itself, is stable to the basic pH conditions used to crystallize
the zeolite. Nitrogen--carbon bonds are particularly effective in
linking the silane modifier to the polymer or polymer segment.
Thus, polymers and silane modifiers effective in forming
carbon-nitrogen bonds are preferred. The ratio of polymer mass of
at least 100 grams per mole of silane modifier is usually necessary
to form intracrystal large micropores and small mesopores. The
volume of the resulting intracrystal textual pores is at least 0.05
cc per gram, more typically 0.10-0.30 cc per gram, and even greater
than 0.5 cc per gram, depending on the zeolite and the method of
preparation. Importantly, for the composition formed by the present
art, the volume of the textural porosity in the 1-10 nm pore size
range far exceeds any mesopore volume due to pores larger than 10
nm. Still further, in the most preferred embodiment of this
invention, the average textural pore size is less than about 7 nm.
Moreover, in the preferred form of the invention, the pore volume
due to the zeolitic framework micropores and the intracrystal
textural pores of the composition amount to at least 80% of the
total pore volume in the pore size range below 50 nm. Concentrating
the pore volume available for catalytic reaction to the size range
below 7 nm, and even below 5 nm for some composition, greatly
improves the catalytic selectivity of the zeolite. In comparison,
all previously reported forms of mesoporous zeolites have the vast
majority of the mesopore volume broadly distributed over pore sizes
greater than 10 nm and little or no textural porosity below 10 nm.
Such broad distributions of textural pores severely compromises the
catalytic selectivity.
[0032] The mechanism by which the silane modified polymer functions
as a porogen is uncertain. The silane modified polymer may bond to
the framework of the growing zeolite in a coiled conformation or it
may form micelles that are stabilized through covalent Si--O--Si
linkages to the growing zeolite surface. In any case, the result is
the encapsulation of the polymer within the zeolite crystal in the
form of a porogen. The removal of the encapsulated porogen through
calcination affords the desired intracrystal textural pores with
the diameters in the large micropore to small mesopore range. The
concentration of porogen within the crystal is sufficient to form a
network of connected textural pores in the desired size range.
EXAMPLES
[0033] The following Examples describe the detailed steps needed to
implement the invention:
Example 1
[0034] This Example describes the synthesis of silane-modified
polymers for use as porogens for the formation of intracrystal
textural pores in zeolites. In order to function as effective
textural porogens, the weight of polymer per mole of silane
modifier was found to be greater than about 100 grams polymer per
mole of silicon. Below this level of silane modification, little or
no textural porosity in the large micropore to small mesopore range
was achieved for the resulting zeolite crystals.
3-glycidoxypropyl-trimethoxysilane (Gelest; Morrisville, Pa.) was
used as the silane modifier. The polymers for modification included
polyethylenimines with average molecular weights of 25000
(Aldrich), 10000, 1800, 600 (Alfa Aesar; Kavkruke, Germany) and
alpha, omega-polypropylene oxides diamines with molecular weights
of about 400, 2000, and 4000. The latter polymers are commercially
available under the trade names Jeffamine D400, D2000, and D4000,
respectively. These combinations of silane modifier and polymer
afforded polymers with C--N carbon bonds that are stable under the
basic pH conditions and temperatures needed for the synthesis of
zeolites. However, the art is not limited to silane modifiers
containing C--N bonds. Any linkage between the silane modifier and
the polymer that is stable to zeolite synthesis conditions are
suitable linkages for the preparation of effective porogens for the
introduction of intracrystalline textural mesopores in
zeolites.
[0035] The polymer and modifier were dissolved into ethanol, which
is used as solvent. The epoxy moiety on the silane modifier and the
primary amino group were allowed to react at elevated temperature
to form C--N between modifier and polymer. In a typical synthesis,
the silane modifier and the polymer were dissolved in ethanol and
the solution was heated in a sealed glass reactor at 100.degree. C.
for 24 hours. The ethanol was then removed under vacuum. The
resulting silane-modified polymer was subsequently used as a
textural porogen in the synthesis of a zeolite.
[0036] For silane modification of polyethylenimine polymers, the
molar ratio of glycidoxypropyl-trimethoxysilane modifier to imine
unit in the polymer was in the range 5 to 10, corresponding to 220
to 2200 grams of polymer per mole of silane modifier. For the
synthesis of silane-modified .alpha.,
.omega.-diaminopolypropyleneoxide polymers, the molar ratio of
silane modifier to amino group in the polymer was 2:1 and the
molecular weight of the polymer was in the range 400 to 4000. In a
typical example of the synthesis of a silane-modified Jeffamine
polymer, 0.50 grams of 3-glycidoxypropyl-trimethoxysilane (2.12
mmol) and 2.12 g of Jeffamine D-4000 (0.53 mmol) were dissolved in
8 g ethanol. The solution was heated to 100.degree. C. for 24 hours
and then the ethanol was removed by applying vacuum in order to
obtain the silane-modifier polymer. The silane-modified polymers
derived from Jeffamine polymers were denoted MP-D400, MP-D2000,
MP-D4000, and those derived from polyethyleneimines were denoted
MP-600(x), MP-1800(x), MP-10000(x), and MP-25000(x), whereas x
presents the N--H/silane ratio.
Example 2
[0037] This Example illustrates the synthesis of a ZSM-5 zeolite
containing uniform textural mesopores using silane-modified
polyethylenimines as the textural porogen. Tetraethylorthosilicate
(TEOS) was the silica source, aluminum isobutoxide was the alumina
source, and tetrapropylammonium hydroxide (TPAOH) was used as the
templating agent for the ZSM-5 framework.
[0038] The silane-modified polymer MP-25000(5) was dissolved in
TPAOH solution. To the resulting solution, was added TEOS and
aluminum isobutoxide under vigorous stirring. The reaction
composition was as follows: 1.00 mole SiO.sub.2 in the form of
TEOS; 0.01 Al.sub.2O.sub.3 in the form of aluminum isobutoxide;
0.37 moles TPAOH; 20 moles H.sub.2O; 4 moles EtOH derived from the
hydrolysis of TEOS; 0.10 silicon in the form of silane modified
polyethyleneimine porogen MP-25000 (5). The mixture was then
transferred into a Teflon-lined autoclave and heated to 150.degree.
C. for 48 hours. The product washed, dried, and calcined at
600.degree. C. for 4 hours. The final product was denoted
MSU-MF1.
[0039] FIG. 1 compares the nitrogen adsorption/desorption isotherms
of mesoporous MSU-MFI with the nitrogen isotherms for conventional
ZSM-5 zeolite. The increase in nitrogen uptake for the mesoporous
MSU-MFI zeolite over the partial pressure range starting at about
0.10-0.15 and ending at about 0.80, along with the associated
hysteresis loop in the desorption isotherm over this partial
pressure range, is attributed to the presence of intracrystal
textural mesoporosity. The conventional form of the zeolite shows
little or no nitrogen adsorption over this partial pressure range.
The nitrogen uptake for both samples below a partial pressure of
about 0.10 is due to the filling of the micropores provided by the
crystalline framework structure of the zeolite. The nitrogen uptake
and hysteresis loop for the MSU-MFI sample above a partial pressure
of about 0.80 is assigned to interparticle mesopores formed between
small zeolite crystals. Note that the pre volume at a partial
pressure of 0.80 is distributed between the framework micropores of
the zeolite (.about.60%) and the intracrystal textural pores formed
by the silane modified porogen (.about.40%). These latter two (2)
types of pore networks account for more than 80% of the total
porosity observed up to a nitrogen partial pressure of 0.99.
[0040] FIG. 2 provides the textural pore size distributions for
MSU-MFI samples prepared in the presence of silane-modified
polyethyleneimine porogens of differing molecular weights, namely:
(A) MP-600(5); (B) MP-1800(5); (C) MP-10000(5); and (D)
MP-25000(5). The BJH pore size distributions were obtained from the
adsorption isotherms over the partial pressure range from about
0.10 to about 0.80. For all the samples, the textural pore size
distribution is narrow with the majority of pores smaller than 5
nm. The average pore diameter increasing from about 2.0 for the
sample made with the lowest molecular weight porogen (MP-600) to
about 3.0 for the sample made with the largest porogen in the
series (MP-25000). FIG. 3 provides a transmission electron
micrograph (TEM) image of a thin-sectioned sample of a typical
MSU-MFI zeolite. The lighter contrast regions of the crystalline
particles clearly show the presence of textural intracrystal
mesopores.
Example 3
[0041] This Example illustrates the synthesis of zeolite Y with
uniform intracrystal textural pores through the use of the
silane-modified polyethylenimine MP-25000(5) as the textural
porogen. Collodial silica (Ludox LS-30), powdered aluminum metal,
tetramethylammonium hydroxide (TMAOH), and sodium hydroxide were
used as reagents for forming the crystalline zeolite framework.
[0042] MP-25000(5) was dissolved in TMAOH. To the resulting
solution, was added the powdered aluminum metal and colloidal
silica under vigorous stirring. The composition of the reaction
mixture was as follows: 1.00 mole SiO.sub.2 in the form of
colloidal silica; 0.23 Al.sub.2O.sub.3 in the form of aluminum
metal; 1.44 moles TMAOH; 113 moles water; 0.10 moles of silicon in
the form of silane modified polyethyleneimine porogen MP-25000(5).
The mixture was then transferred into a Teflon-lined autoclave and
heated at 100.degree. C. for 96 hours. The product washed, dried,
and calcined at 600.degree. C. for 4 hours. The final product was
denoted as MSU-Y.
[0043] FIG. 4 provides the nitrogen adsorption/desorption isotherms
of the MSU-Y zeolite product in comparison to conventional zeolite
Y. The nitrogen uptake by the MSU-Y zeolite in the partial pressure
region from about 0.05 and about 0.80 is due to the filling of
intracrystal textural pores. As in the case of the conventional
zeolite Y, the nitrogen uptake below a partial pressure of about
0.05 is due to the filling of micropores in the framework of the
crystalline zeolite. The conventional Y zeolite exhibits little or
no additional nitrogen uptake beyond a partial pressure of 0.05 as
expected for the absence of textural mesoporosity. Note that for
the MSU-Y sample, about 25% of the total nitrogen uptake volume at
a partial pressure of about 0.80 is due to filling of the textural
intracrystal pores. The liquid pore volume due to the intracrystal
textural at this partial pressure is at least 0.1 cc per gram, as
estimated by subtracting the pore volume due to the microporous
zeolite framework from the total pore volume at this same partial
pressure. The liquid pore volume due to intracrystal textural
porosity is larger than 0.05 cc per gram, more typically between
0.1 and 0.3 cc per gram and occasionally in excess of 0.5 cc per
gram. Moreover, from the isotherms in FIG. 4, more than 95% of the
total nitrogen pore volume at a partial pressure of 0.99 is due to
the filling of framework micropores and textural mesopores of the
zeolite and less than 5% of the total pore volume is due to the
filing of extra crystalline textural pores between the zeolite
crystals.
Example 4
[0044] This Example illustrates the synthesis of mesoporous ZSM-5
using silane-modified Jeffamine surfactants MP-D2000 and MP-D4000
and as the textural porogens. The purpose of the example is to
demonstrate that the average textural pore size can be tuned to a
value between 3.5 and 5.5 nm while keeping the width of the
textural pore size distribution below about 10 nm.
[0045] For the preparation of mesoporous MSU-MFI zeolite with
MP-D4000 as the porogen, the polymer was dissolved in TPAOH along
with ethanol. To the resulting solution was added aluminum
isobutoxide as the aluminum source and TEOS as the silicon source
under stirring to afford a reaction mixture with the following
composition: 1.00 mole of SiO.sub.2 in the form of TEOS; 0.01 mole
of Al.sub.2O.sub.3 in the form of aluminum isopropoxide; 0.37 mole
TPAOH; 20 mole of H.sub.2O; 8 mole of EtOH from the hydrolysis of
TEOS and the addition of neat ethanol; 0.025 mole of silicon in the
form of silane modified MP-D4000 porogen. The reaction mixture was
then heated to 100.degree. C. for 96 hours. Solid product was
collected by filtration, washing, drying followed by calcination at
600.degree. C. for 4 hours.
[0046] For the preparation of the MSU-MFI zeolite with MP-D2000 as
the textural porogen, the procedure was similar to the procedure
described above using MP-D4000, except that the composition of the
reaction mixture was as follows: 1.00 mole of SiO.sub.2 in the form
of TEOS; 0.01 mole of Al.sub.2O.sub.3 in the form of aluminum
isopropoxide; 0.37 mole TPAOH; 20 mole of H.sub.2O; 4 mole of EtOH
from the hydrolysis of TEOS; 0.040 mole of silicon in the form of
silane modified MP-D2000 porogen and the reaction was carried out
at 125.degree. C. for a period of 48 hours.
[0047] FIG. 5 provides the nitrogen adsorption/desorption isotherms
of MSU-MFI prepared with silane-modified Jeffamine polymers
MP-D4000 and MP-D2000, along with the BJH pore size distributions
obtained from the adsorption isotherms in the partial pressure
range from about 0.10 to about 0.80. The larger MP-D4000 porogen
afforded an average intracrystal textural porosity of about 5.5 nm,
whereas the smaller MP-D2000 porogen provided an average textural
pore size of about 3.5 nm. For both materials, the intracrystal
textural pore size distribution is confined to pore size values
below 10 nm. Also, for both materials, the intracrystal textural
pore volume below a pore size value of 10 nm, together with the
framework pore volume, accounts for 85 to 90% of the total pore
volume measured at a partial pressure of 0.99.
Example 5
[0048] This Example illustrates the use of a low molecular weight
silane-modified porogen for the preparation of a zeolite containing
intracrystal textural porosity in the supermicropore range between
1.0 and 2.0 nm. For silane modified Jeffamine D400 polymer, denoted
MP-D400, there are four (4) silane groups per mole of polymer, so
that the mass of polymer per mole of silane group is near 100.
[0049] For the preparation of the MSU-MFI zeolite with MP-D400 as
the textural porogen, the procedure was similar to the procedure
described in Example 4. The compositions of the reaction mixtures
were 1.00 mole of SiO.sub.2 in the form of TEOS; 0.01 mole of
Al.sub.2O.sub.3 in the form of aluminum isopropoxide; 0.37 mole
TPAOH; 20 mole of H.sub.2O; 4 mole of EtOH from the hydrolysis of
TEOS; 0.050 or 0.10 mole of silicon in the form of silane modified
MP-D400 porogen. The reaction was carried out at 150.degree. C. for
a period of 48 hours. The solid produces were collected by
filtration, washed, and dried followed by calcinations at
600.degree. C. for 4 hours.
[0050] Both reaction products exhibited Type I nitrogen adsorption
isotherms indicative of the presence of microporosity. The BET
surface areas determined from the nitrogen adsorption isotherms
were 887 and 955 square meters per gram for the MSU-MFI products
prepared from reaction mixtures containing 0.050 and 0.10 mole of
silicon in the form of silane modified MP-D400 porogen,
respectively. These values are substantially larger than the 400 to
600 square meters per gram BET surface areas observed for the
mesoporous MSU zeolites prepared in Examples 2, 3, and 4 in the
presence of higher molecular weight porogens. Also, conventional
MFI zeolite has a surface area of about 350 square meters per gram,
due primarily to the micropores of the crystalline framework. Thus,
the exceptionally high BET surfaces observed for the products of
this Example indicate that the textural pores formed by the small
silane modified MP-D400 porogen also are in the micropore range
below 2.0 nm, but larger than the 0.55 nm pore size of the
crystalline zeolite framework.
[0051] While the present invention is described herein with
reference to illustrated embodiments, it should be understood that
the invention is not limited hereto. Those having ordinary skill in
the art and access to the teachings herein will recognize
additional modifications and embodiments within the scope thereof.
Therefore, the present invention is limited only by the claims
attached herein.
* * * * *